Fluid heater



Aug. 17, 1948. E. G. BAILEY EIAL 2,447,305

FLUID HEATER Filed Sept. 16, 1943 1 5 Sheets-Sheet 1 I INVENTORS frz/m G. Bailey f BY Ea/ph M HardgroI/e A TTORNEY I E. G. BAILEY ETAL Aug. 17, 1948.

FLUID HEATER 5 Sheets-Sheet 2 Filed Sept. 16, 1943 INVENTORJ Err/in G Bai/e BY Ralph M y Hardy/Z;

ATTORNEY Aug. 17, 1948. E. e. BAILEY ETAL FLUID HEATER Filed Sept. 16, 1943 5 Sheets-Sheet 3 km 3525K L wmEm K an f y 1 5w w wd m m in MB A GM fl1 ID! m R Y B Aug. 17, 1948. E. G. BAILEY arm. 2,447,305

FLUID HEATER Filed Sept. 16, 194: 5 sheets-sheets INVENTORJ Erw'n GBai/eg 2 BY Ralph M Hardgrave ATIORNE Y atenteii Aug. 17, 1948 FLUID HEATER Ervin G. Bailey, Easton, Pa., and Ralph M. Hardgrove, Westfleld, N. 1., assign era to The Babcock & Wilcox Company, Rockleigh, N. J., a corporation of New Jersey Application September 16, 1943, Serial No. 502,580

24 Claims. 1

The present invention relates in general to the construction and operation of fluid heaters of the type in which a heat transfer medium is emplcyed consisting of a fluent mass or column of refractory material which is first heated by the passage of a heating fluid in heat transfer relation therewith, and then cooled by contact with a second fluid to be heated, and more particularly to fluid heaters of the character described in which the mass or column of heat transfer material flows downwardly through superposed heating and cooling chambers connected by a neck or throat of reduced flow area.

Recuperative fluid heaters in which the fluid to be heated is passed through or around tubes or plate passages exposed to a heating fluid on their opposite wall surfaces are limited in the fluid temperatures attainable by the heat and corrosion resisting properties of the material forming the tubes or plates. Ordinary iron or steel.

for example, having a melting point "of" 2700-2900 F. oxidizes relatively rapidly at metal temperatures above approximately 950 F., and such ferrous structures are ordinarily limited to use under metal service temperatures below 900 F. For higher service temperatures, and particularly where the metal parts are subjected to internal or external pressure stresses, alloy steels and special heat-resisting alloys are universally used, in view of the rapidity with which carbon steels are oxidized and lose strength at high temperatures. Such alloy steels and heat resisting alloys however are relatively expensive and, when such materials are in great demand, relatively unavailable for fluid heater construction. Furthermore, such alloy steels and heatresisting alloys also have upper use temperature limits for economic long life operation of approximately 1500 F; Consequently where parts are exposed to even higher temperature conditions, the use of 'such alloy steels and heat-resist-. ing alloys is not practicable. Tubular fluid heaters however have the important characteristics of afl'ording continuous heating of the fluid to be heated and complete separation of the heated and heating fluids.

Regenerative heaters of the reversing'type in which the fluid to be heated is intermittentlypassed through a checkerwork or the interstices v of a bed of refractory material which is heated during intervening periods by a heating fluid are capable of heating a fluid to a relatively high temperature, but are characterized by a periodic fluctuation in outlet temperature of the fluid being heated during each heating cycle, contamination of the fluid to be heated by the heating fluid and vice versa due to the difliculty of maintaining proper sealing devices under such operating conditions and the presence of residual fluid in the bed or checkerwork, or as an alternative purging of the bed or checkerwork with steam subsequent to each heating cycle with a resulting loss in emciency and lowering of the checkerwork and heated fluid temperatures attainable. and also a relatively low overall thermal efficiency.

Fluid heaters in which a fluent mass or column of refractory material is passed through successive heating and cooling chambers, and successively heated by a heating fluid and cooled by heat transfer to a fluid to be heated, have been heretofore proposed for uses in which the desired flnal temperature of the fluid to be heated is in or excess of the temperatures for which ordinary or alloy steel tubes can be used. Such proposed applications have been usually characterized by an inherently low fluid heating capacity due to the low maximum fluid flow velocities permissible therein without excessive lifting and carryover of the heat transfer material with the heating and heated fluids, contamination of the fluid to be heated by the heating fluid or vice versa, the inclusion of metallic parts in locations in which they are exposed to temperatures above the temperature which such parts could safely withstand, the use of a refractory heat transfer material which tends to fuse or disintegrate under the intended operating conditions, and/or a relatively low overall thermal efllciency. For the foregoing reasons, little or no commercial use has been made of fluid heaters of this type,

The general object of this invention is the provision of a method of and apparatus for heating a fluid by heat transfer from a fluent gaspervioqs mass or column of refractory heat transfer material which are characterized by the continuity and uniformity of heatingand heat absorption and the capacity for separation of the heated and heating fluids present in recuperative tube and plate heaters. A further and more specific object ofthis invention is the provision as the fusing temperature, of the refractory.

materials employed. with little or no contamination of the fluid being heated by the heating fluid employed and vice versa, without subjecting any included metallic parts to unsafe operating temperatures or requiring special corrosion and heat resistant alloys for operating temperatures above 900 F., and with a relatively high overall thermal efflciency. A further object is the provision of a method and apparatus of the character described permitting relatively high fluid flow velocities through the mass of refractory heat transfer material without interruption of the mass movement or carryover of the heat transfer material into the outlet passages of the apparatus. Another object is the provision of an improved neck or throat construction and associated control system permitting a free gravitational flow of the refractory heat transfer material, while effectively restricting or preventing the fiow of fluid therethrough. Another object is the provision of an effective method of and apparatus for automatically controlling the fluid pressure and temperature conditions in the various parts of the apparatus.

The various features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention; its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated and described.

Of the drawings:

Fig. 1 is an elevation partly in section of a pilot plant unit constructed in accordance with the invention, the structural supports bein omitted for purposes of clarity; j FiFig. 2 is a plan view of the apparatus shown in Fig. 3 is an enlarged sectional elevation ofa portion of the apparatus shown in Fig. 1;

Fig. 4 is a horizontal section taken on the line H of Fig. 3;

Fig. 5 is an enlarged view of part of the ap-' paratus shown in Fig. 3;

Fig. 6 is a diagrammatic view of one form of control system;

Fig. 7 is a diagrammatic view of a modified control system;

-Fig. 8 is an enlarged view oi a modified construction of part of the apparatus shown in Fig. 3; and

Fig. 9 is a horizontal section taken on the line 99 of Fig. 8.

While in its broader aspects this invention is adapted for the use of liquid and gaseous fluids asthe heated and/or heating fluids, the method and apparatus of the invention are particularly adapted for the use of high temperature gases as the heating fluid and a gaseous fluid, such as a gas, vapor or finely divided solid in suspension, as the fluid to be heated to a high temperature.

The fluid heating unit illustrated in the drawings is particularly constructed and designed for the use of gaseous heating and heated fluids under pressure, and as shown comprises as its main column consisting of small pieces 01 refractory heat transfer material I to be heated by high temperature gases while passing therethrough, a connected subiacent heat absorbing or reaction chamber Ii arranged to receive, and normally substantially completely filled with, heated refractory material H from the upper chamber and in which the heated refractory material is utilized for heating a gaseous fluid to a predetermined temperature, an elevator l2 receiving the cooled refractory material from the lower chamber ii, and returning it to the upper part of the upp r chamber i0, and a control system for regulating operating conditions in the upper and lower chambers The upper or heat transfer material heating chamber I8 is of vertically elongated circular horizontal cross-section and formed by a substantially cylindrical as-tight steel casing iiv lined with high temperature flrebrick ii. A conical plate i1 lined with refractory II' forms the root of the chamber l0 and contains a heatin as outlet pipe i8 in which a control damper I9 is located. The damper i5 is controlled by a manually or automatically operable mechanism I 8' here- I inafter described to regulate the rate 01 outflow of heating gases and thereby the gaseous pressure in the upper chamber. An inlet 20 for the refractory heat transfer material is located in the side of the chamber Ill adjacent its upper end. A substantially annular refractory walled combustion chamber 2! surrounds the lower end or the chamber ill and provides a source of high temperature heating gases therefor. As shown in Figs. 3 and 4, the combustion chamber has arcuate outer walls 22, an annular arched roof 23, floor 24, and a circular vertical bridge wail 25,1111 preferably formed 01' high temperature flrebrick. The steel casing i5 is continued downwardly. around the combustion chamber to provide a gas-tight wall construction therefor. The flrebrick lining I5 is advantageously shaped to make the chamber iii of larger cross-sectional area in the chamber section containing the upper Part of the refractory mass than in the section containing the lower portion of the mass, the lining being progressively flared upwardly at an intermediate point. a i

The lower end of the lining I6 is defined by an annular refractory member 21 having an inward- .ly and downwardly projecting section 21' and wholly or partly spaced from the top of'the bridge wall 25 to define an annular or substantially annular flow passage 28 therebetween forming the heating gas inlet from the combustion chamber 2|. As shown in Fig. 3, the member 21 is formed by a sectional angle-shaped ring having suitable service water connections and serving to. support the superposed firebrick Hi from the casing IS. The ring is preferably constructed to have the cooling water flow first throughthe inwardly and downwardly projecting ring section 21' and then successively through the outer sections of the ring 21. The ring 21 is wholly spaced from the top of the bridge wall 25 to define an annular" spilling of the heat transfer material into thecombustion chamber 2|, since the position of the lower end of the ring section 21' determines the level of contact of the heat transfer material with the inner side of the bridge wall 25 when the material assumes its approximate natural angle of repose as will occur when the contacted side of the bridge wall is vertical and there is no gaseous lifting effect on the material at that point. An upwardly flaring bridge wall shape at and immediately below the contact level of the heat transfer material would tend to retard the downward flow of the material by forming a stagnant portion of the mass in this area, which stagnant portion would be continuously contacted by the entering high temperature gases from the combustion chamber and liable to become overheated.

While various fuels can be burned in the annular combustion chamber 2| to provide the desired supply of high temperature gases, or flue gases from other apparatus introduced as a source of heat, a gaseous fuel is used in the embodiment illustrated. For this purpose rectangular burner ports 30 are tangentially arranged in diametrically opposite parts of the combustion chamber wall 22. Tuyere blocks 3| are supported in the ports 30 in spaced relation with the sides of the corresponding port to form passages 32 therebetween. A combustion air casing 33 having an air supply connection 34 is arranged at the outer side of the block 3| for supplying combustion air to the the tuyre block passage 35. A premix type Venturi-shaped gas burner 36 having a spark plug 31 mounted therein is symmetrically arranged in the casing 33 at the outer side of and relative to the block passage 35. A valve controlled fuel gas supply connection '38 provides a fuel supply to each burner 36. A second casing 39 surrounds the inner part of the casing 33 and opens to the passages 32. A valve controlled supply pipe 40 permits additional combustion air or recirculated flue gas to be supplied in variable amounts to the casing 39 and passages 32 for tempering the heating gases generated.

The circular cross-section of the upper chamher is progressively decreased from about midway the height of the bridge wall to the upper end of a neck or throat passage 42 connecting the chambers l and H, by the addition and shaping of initially lastic high temperature ma-; terial 43 in this section. The throat 42 is formed by sectional refractory blocks 44 supported on the arched roof 45 of the lower chamber and cooperating to define a. downwardly slightly flaring throat of a predetermined length, minimum circular cross-section and flare. The permissible minimum-diameter, flare and length of the throat will depend upon the size and shape of the heat transfer material elements, the desired pressure drop in the throat, and the location of the gas outlet from the lower chamher. In accordance with this invention, the throat length can be considerably shorter than those in fluid heaters of this type heretofore proposed.

The lower or heat absorbing chamber II is shown as of uniform circular horizontal crosssection and also formed by a cylindrical steel casing is lined with high temperature flrebrick it except at its lower end, which is formed by an annular metallic casing having a valve controlled fluid inlet 52 in its outer side and a screen 53 defining its inner side. A gaseous 6 fluid outlet 54 is formed in the upper part of the chamber wall above the normal level of the mass of material therein. The chamber II has a downwardly tapered hopper 55 below the casing 5i and opening into a discharge pipe 58; The discharge of material from the pipe 56 is controlled-by an adjustable inclined gate 51 at the entrance end of a housing 58 for a variable speed fluid sealing materialdischarge device, such as a multi-pocket rotary feeder 59 driven by a variable speed electric motor 60 through a speed reducer 6i, as shown in Figs. .1 and 5. The gate 51 acts as an inverted weir to limit the discharge of refractory material H to the feeder 58 to a level at which the feeder pockets formed by blades arranged tangentially to the feeder shaft will only be partly filled as they pass through the heat transfer material present. Each feeder blade has a raised lip 59' on its leading edge to hold the pieces of/material in the pockets. With only partly filled pockets, the clearance between the adjacent surface hardened portions of the feeder blade lips and housing may be made a minimum to form a gaseous fluid seal at this point. The material in the feeder pockets tends to level off as each lip 69' approaches the upper sealing position, thus eliminating any danger of'material jamming between the feeder blades and housing. The feeder thusprovides a gaseous fluid sealing effect at the material discharge end in addition to the-sealing effect of the column of material in the hopper 55 and pipe 56.

The feeder housing 58 is provided with a valvecontrolled pipe connection 58' between the gate and feeder and through which steam or other inert gas under pressure can be introduced when leakage losses of amore valuable vapor or gas being heated are to be minimized. The steam so introduced flows upwardly below the gate 51, displacing and removing any residual gas or vapor from the refractory material in the housing 58 and pipe 56 and returning it to the lower chamber II.

The selection of a suitable heat transfer material I4 is highly important and will depend upon the operating conditions to which the material will be subjected, and particularly the range of operating temperatures, the character of the heating and heated fluids, and the desired pressure, fluid flow velocities and heat transfer efllciency conditions to be maintained. The material selected should be of a refractory character suitable to withstand the wide range of temperatures which it will encounter in normal operation without spalling or cracking. While this invention in its broader aspects contemplates the use of a. relatively -wide range of refractories, such as ceramic refractories and corrosion resistant alloys and alloy steels, in small pieces of regular or irregular shape, such assized grog. pebbles and crystals of mullite, silicon carbide, alumina and other refractories, a charge consisting mainly of small pieces of refractory material of uniform size and shape is preferably used to thus maintain substantially uniform fluid flow passages and consequently a substantially uniform fluid flow and heat transfer effect throughout the cross-section of each chamber. The shape of the refractory pieces should be conducive to a rapid movement of the heat transfer material and accordingly smooth surfaced spherical pieces are preferred. The refractory selected should include no constituent which would tend to fuse in the normal operating temperature range and cause the pieces 'to agglomerate, and thu obstruct the material movement. For high rates of heat transfer, the refractory material should preferably have a high specific heat and a high thermal conductivity. A high density material is also desirable to permit the use of refractory pieces of a size which will allow a relatively high fluid velocity through each chamber and a high heat capacity for the fluent masses of material therein, while preventing lifting and carryover of the material with the outgoing fluids. By way of example and not of limitation, we have found the following ceramic refractory compositions suitable as heat transfer material for heating air to temperatures approximating 2000 F.:

Composition A Percent by weight Calcined cyanite (35 mesh) 50 Raw bond clay 35 Raw brick clay 15 A dextrine binder consisting of 1% by weight of the other ingredients is added to the above mix and the composition molded into pellets or balls and fired to 2850 F.

Composition B Percent by weight Calcined Georgia kaolin (40 mesh) 67 Raw Georgia kaolin 33 of a stream of air of a density equivalent to atmospheric air at 60 F. through such a pellet mass up to 10 ft. per second per unit of projected area without carryover, i. e. a mass flow of approximately 2800 lbs. per sq. ft. per hour. The pellet size employed will depend upon the desired flow velocities and fluid pressure drops in the chambers I and II, and in general, the pellets should be spherical or substantially spherical and of the same size with a diameter preferably in the range of /4- The feeder 59 empties into an inclined outlet pipe 62 having an expansion joint connection 63 with both the feeder housing and a pellet inlet box 64 for an elevator casing 65. The box 64 has a door 66 in its top for adding pellets to the system and a second door 66' in its lower part for their removal. By this arrangement pellets may be added or withdrawn from the system to regulate the depth of the pellet mass in the upper chamber l0 and thereby the temperature of the pellets leaving the upper chamber, and consequently regulate the temperature of the vapor or gas leaving the lower chamber without changing the supply of heating gases to the upper chamber.

The elevator casing 65 is of circular cross-section throughout its height and made of steel plate welded gas-tight. The elevator l2 illustrated is of the slow speed continuous bucket type, having overlapping buckets 61 which are only partly filled with pellets at the normal rate of pellet circulation. The elevator is driven by an electric motor 68 through a speed reducer and a chain and sprocket connection to the elevator head shaft. The elevator buckets empty into a discharge pipe 69 having a lower side outlet and ill a bottom screen II for permitting dust and broken pellets to separate and drop into a bin 12, as it is desirable to keep the masses of heat transfer material of a uniform pellet size and shape and thus maintain uniform gaseous fluid flow passages therethrough. The outlet 16 is connected to the pellet inlet 20 of the upper chamber by a zig-zag pipe 13 and expansion Joints ll to provide the desired angle of approach to the pellet inlet.

In the normal operation of the apparatus described, the chambers l0 and I I and throat 62 are fllled with refractory pellets of the desired size and shape to form a continuous fluent mass with approximately the levels indicated in Fig. 3. The feeder and elevator are controlled so that the pellets move continuously downward through the upper chamber, throat and lower chamber portions of the pellet mass or column to move downwardly continuously as long as the feeder is in operation. Fuel is fired in the combustion chamber 2| and the heating gases generated flow through the annular inlet 28 into the lower part of the upper chamber l0, passing upwardly through the interstices in the pellet mass in intimate counterflow contact with the descending pellets, whereby the pellets are eil'ectively heated to a high temperature and the gases leave through the heating gas outlet 18 at a relatively low temperature. The highly heated pellets move downwardly in the column through the throat 42 into the chamber II. The gaseous fluid to be heated, such as air, steam, naphtha, etc., is introduced into the annular casing 6| under a predetermined pressure, passing through the screen 53, and upwardly through the interstices between the descending pellets in the chamber II where it is heated in counterflow heat transfer, and passes out at the desired temperature through the outlet 54. The pellets discharge from the hopper 55 and pipe 56 through the adjustable gate 51 to the rotary feeder 69, the speed of which is regulated to provide the desired rate of descent of the pellet column. The pellets are continuously discharged through the pipe 62 and elevator inlet box 64 to the elevator buckets 61, which return the pellets to the upper chamber inlet 20 through the pipes 69 and 13. The fluid pressure in the elevator casing will be the same as the gas outlet pressure in the upper chamber due to the unobstructed flow connection therebetween. A rotary feeder, seal similar to the feeder 59 may be included in the inlet pipe if desired, and in that event operated at a speed corresponding to a greater capacity than the feder 59 so that the pellets would never fill up the pipe 10 and spill back into the elevator casing.

The apparatus illustrated is designed and constructed for high capacity operation and high gas or vapor velocities through the pellet masses in the upper and lower chambers with little or no gas or vapor leakage through the throat between the two chambers. The fluid pressure drop through each chamber will vary with the rate of operation of the apparatus, but due to the size and shape of the pellets will be relatively low throughout the operating range. In view of the substantially shorter length or height of the pellet column in the throat 42 than in the chambers l0 and I l, the gaseous fluid flow resistance through the throat will normally be substantially less than in either of the chambers. I

In order to minimize leakage between the upper auasoo and lower chambers, the throat 42 is made with the smallest diameter which will permit the pellets to flow therethrough without danger of bridging over in the throat. The downward flare of the throat also aids in preventing bridging therein. For example, withspherical pellets of the described ceramic composition approximately one-half inch in diameter and balanced pressures in the two chambers, a minimum throat diameter 9 Oct. 18, 1943, which has issued as U. SJatent No.

2,417,049. An air loading pressure is established by the controller" which is representative of the pressure diiferential and transmitted to a suitable standardizing relay 99, such as disclosed in U. S. Patent 2,098,914, which establishes a control pressure transmitted to a suitable selector valve 94, such as disclosed in U. 8. Patent- 2,202,485, and thence to a servo-motor 95 of the damper operating mechanism l9 to operate the damper I! in the heating gas outlet ID. The arrangement is such that upon a departure of the pressure difierential from the desired value, an immediate .and proportional change takes place in the position' of the damper 19 in a direction tending to restore the pressure condition in the upper chamber to the desired relative value. Thereafter the standardizing relay operates to gradually position relative chamber pressures are advantageously employed. For example, such provisions are operable to maintain balanced pressure conditions in the upper and lower chambers at opposite ends of the throat so that there will be no fluid flow through the throat. Where it is essential that there be no contamination of the lower chamber fluid by the, heating fluid, the control system is operated sothat the bottom of the upper chamber is maintained at a pressure slightly less than the pressure of the fluid leaving the top of the lower chamber, so that a slight leakage of fluid upwardly from the lower chamber through the throat into the upper chamber will be maintained. Where such contamination is immaterial, the control system can also be operated to provide a leakage of heating fluid downwardly through the throat.

Where however no fluid flow through the throatbetween the chambers is desired, absence ofcontamination in either chamber can be insured by the introduction of a small amount of a gas, such as steam, which is inert with respect to the treated'fluid, into the upper part of the throat through a valve controlled pipe 16. With balanced pressure conditions in the two chambers, the steam will flow in both directions in the throat. With, unbalanced plressure conditions, the steam introduced tends to form a fluid seal maintaining the chamber atmospheres separate.

As diagrammatically illustrated in Fig. 6, the control system for theapparatus includes a differential pressurecontrol responsive to the pressure differential at vertically spaced points in or at opposite sides of the throat 42 for regulating the exit of gaseous fluid from the upper or lower chambers to establish the desired relation between the pressure conditions in the two chambers. Damper regulation of the heating gas outflow from the upper chamber is ordinarily preferred because of the lower temperature conditions at that point; The differential pressure control diagrammatically illustrated comprises a transmitter 80 responsive to the pressure differential between the lower part of the upper chamber 10 and'the gaseous fluid space at the top of the lower chamber II, and a differential pressure recorder controller 82. The instrument 82 also records changes in fluid flow entering the lower chamber by means of a second transmitter 8| responsive to such variations. 80 and 9| are similar in construction to that shown in a 'copending application of Ervin G. Bailey and Paul S. Dickey, Serial No. 506,630, filed the damper l9 until the pressure in the upper chamber reaches the predetermined desired value. The selector valve 84 provides a convenient means for transferring operation of the damper 9 from automatic to manual control, if that is desired in starting up or on shutting down the unit.

The supply of combustion air to the combustion chamber 2| is controlled by a fuel-air ratio controller 90 in which a bell crank lever 9| is jointly actuated by diaphragms 92 and 93, the diaphragm 92 being responsive to the differential between the combustionchamber pressure and that in the fuel gas line, while the diaphragm 93 is responsive to the diiferential between the combustion chamber pressure and that in the combustion air supply pipe. The movable valve member of a pilot valve 94, such as disclosed in U. S. Patent- 2,054,464, is actuated by the bell crank lever, so

' that a loading pressure is established correspond.-

ing to the ratio of the air-gas pressure. The loading pressure so established is transmitted to a a standardizing relay 9!, similar to the relay 93,

which establishes a control pressure transmitted through a selector valve 99 to a diaphragm operated control valve 91 in the combustion air supply pipe to vary the amount of combustion air supplied to the burner casing in response to variations in the fuel gas-air ratio. Manually operated control valves 98 and 99 are located in the fuel gas supply pipe 38 and pipe 40 respectively to regulate the flow through those pipes. A thermal responsive element I00 is located in the gaseous fluid outlet 54 and connected to a temperature recorder l0 I.

The transmitters The foregoing controls may be supplemented .where the flow of gaseous fluid to be heated is fluctuating by automatically controlling a valve in the lower chamber inlet to maintain the desired pressure at the outlet 54, and also by regulating the supply of fuel gas to the combustion chamber to control the temperature of the heated gaseous fluid leaving the lower chamber.

A further control of vapor outlet temperature is provided by regulating the speed of the rotary feeder 59 in response to deviations of the vapor outlet temperature from a predetermined value. The consequent control of the rate of pellet circulation determines the time of contact between the pellets and the heating gases as well as with the gas or vapor to be heated. A plurality of fluid inlets can also be provided at different levels in the lower chamber H to vary the length of con- 11 for superheating steam from a temperature of 260 F. and 12.1 p. s. i. entering the lower chamber to a final temperature of 1800 F. at the outlet 54, the heating gas temperature entering the upper chamber being 2350 F. and at the gas outlet l8 being 800 F.

In Fig. 7 we have illustrated a modified control systemparticularly designed for the superheating of a fluctuating supply of steam to high temperatures. This system includes means for regulating the damper I! in response to variations in the pressure differential across the throat 42 similar to those illustrated in Fig. 6. Also an airgas ratio control of the combustion air supply similar to that illustrated in Fig. 6,'except that the ratio controller diaphragm 92 is responsive to fuel gas flow variations and the diaphragm 93 to changes in air flow in the pipe 34.

In the Fig. 7 control system, additional automatic controls are provided including a steam pressure controller I responsive to the steam pressure at the steam outlet end of the lower chamber II which operates through a standardizing relay I06 and selector valve ifll to automatically regulate a control valve I08 in the steam supply line 52.

:Variations in the steam outlet temperature as measured by the thermal responsive element I00 and recorder i Mare employed to automatically regulate a control valve H0 in the. fuel gas line 38 through a standarizing relay I I I, selector valve 2 and three-way solenoid valve H3, to thus maintain the vapor outlet temperature at a predetermined value by regulation of the fuel supply.

In the construction described, the flow areas of the chambers i0 and II in the sections occupied by the pellet masses are preferably proportioned to maintain the maximum flow velocities permisshort of the lower end of the casing, leaving an annular opening I54 therebetween for draining the casing of any dust and broken pellets passing outwardly through the 'screen. An annular resible with-the type of refractory heat transfer to be thrown into the gaseous fluid outlets i8 or I4 and carried out with the discharging, gas or vapor. The lifting eflect of the ascending gaseous fluid streams can be minimized by providing a uniform distribution of the gaseous fluid throughout the entire flow area of the Pellet masses and. by increasing the available flow area in the upper part of each chamber. As shown in Fig. 3, the cross-sectional area of the chamber In is substantially increased in the section normally occupied by the upper part of the pellet mass therein. The narrowed chamber cross-section at the level at which the heating gases enter the upper chamber facilitates their uniform distribution throughout the flow area of the pellet mass therein and the maximum heating temperature of the pellets. A similar construction may also be used for the lower chamber i I.

In Figs. 8 and 9, we have illustrated a modified construction for the chamber i I. In this construction, the refractory blocks 44 defining the connecting throat 42 are chamfered at their lower ends to increase the volume of the space above the mass of heat transfer material in the lower chamber. An improved construction of the lower chamber fluid inlet is also illustrated in which both the inlet casing HI and screen I53 have an inverted frusto-conical form. the screen having an approximately 15 taper and the casing a 30 taper to the vertical. The casing l5i is continued downwardly to merge into the discharge pipe 56, while the screen I53 terminates ties will cause a violent disturbance of the upper part of the pellet masses which may cause pellets fractory baille IE5 is arranged at the upper end of the screen to deflect the fluid to be heated, whichenters the casing through the fluid supply pipe I52, downwardly around the subjacent portion of the screen. With this arrangement, a substantially uniform static pressure condition will exist throughout the casing iii, providing a substantially uniform distribution of the fluid to be heated into the pellet mass.

The described method and apparatus can be used for continuously'heating a gaseous fluid up. to temperatures approaching the fusing point of the heat transfer material. Such temperatures are substantially higher than the maximum obtainable with recuperative plate or tubular heaters constructed of heat resistant alloy metals, and slightly higher than the maximum obtainable with refractory checkerworlr'. It has decided advantages over the latter in the lesser amount of space occupied, absence of change-over valves,

elimination of alloy materials, and particularly in its continuity of operation and capacity for complete separation of the heating gases and gaseous fluid heated. A wide variety of gases and vapors may be heated with little or no change in the construction or method of operation.

While in accordance with the provisions of the statutes the best forms of the invention now known have been illustrated and described herein, those skilled in the art will understand that changes may be made in the method and in the form of the apparatus disclosed without departing from the spirit of the invention covered by the claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

In the claims, the term refractory heat transfer material is intended to cover generically any suitable refractory material of regular or irregular shape or size, whereas the term pellets" is intended to cover generically small pieces of heat transfer material of generally rounded contour and formed of any suitable natural or artificial refractory composition and having a maximum dimension not less than A" and not more than 1".

We claim:

1. A fluid heater comprising an upper chamber enclosing a fluent gas-pervious mass of refractory heat transfer material and having a heat transfer material inlet and a heating fluid outlet at its upper end, means for introducing a heating fluid directly into the lower part of said upper chamber in heat transfer relation with the mass of heat transfer material therein, a lower chamber enclosing a fluent gas-pervious mass of refractory heat transfer material and having a heat transfer material outlet at its lower end, said lower chamber having an inlet at its lower end for a fluid to be heated therein and a heated fluid outlet at its upper end above the mass of heat transfer material therein, means forming a vertically elongated structurally unobstructed throat passage of reduced cross-section between and directly connecting said upper and lower chambers and enclosing arcontinuous fluent gaspervious mass of refractor heat transfer material connecting said masses of heat transfer material in said upper and lower chambers, said last named means including a tubular refractory member extending downwardly into said lower chamber to upper end, means for introducing high tempera ture heating gases directly into the lower part of said upper chamber in direct contact with the mass of heat transfer material therein, a lower chamber enclosing a fluentgas-pervious mass of refractory heat transfer material and having a heat transfer material outlet at its lower end, said lower chamber having an inlet at its lower end for a fluid under pressure to be heated therein and a heated fluid outlet at its upper end, a vertically elongated structurally unobstructed passage -formlng a throat of substantially reduced cross-section between and directly connecting said upper and lower chambers and enclosing a continuous fluent gas-pervious column of refractory heat transfer a material connecting said masses of heat transfer-material in said upper and lower chambers, and means receiving heat transfer material from said lower chamber .material outlet and returning said material to said upper chamber material inlet including a material discharge device constructed to form a fluid seal for said lower chamber material outlet, a

variable speed motor for variably driving said,

material discharge device to. control the rate of circulation of heat transfer material, and means for varying the discharge temperature of the heat transfer material independently of the rate of introduction of heating gases into said upper chamber.

3. A fluid heater comprising an upper chamber i4 and having a heat transfer material outlet at its lower end, sald lower chamber having an inlet at its lower end for a gaseous fluid under pressure to be heated therein and agaseous fluid outlet at its upper end above the mass of heat transfer material therein, a vertically elongated unobstructed passage forming athroat of substantially reduced cross-section between said upper and lower chambers and enclosing a fluent column of refractory heat transfer material connecting said masses of heat transfer material in said upper and lower chambers, elevator means receiving heat transfer material from said lower chamber material outlet and returning said mate rial to said upper chamber material inlet including a material discharge device constructedto form a substantial gaseous fluid seal for said lower chamber material outlet, and means for introducing a second gaseous fluid between the material discharge side of said discharge device and said gaseous fluid inlet to said lower chamber at a pressure higher than'said'flrst named gaseous fluid inlet pressure.

5. A fluid heater comprising an upper chamber enclosing a fluent mass of refractory heattransfer material and having a heat transfer material inlet and a heating fluid outlet at its upper end, means for introducing a heating fluid into said upper chamber in direct contact with the mass of refractory material therein, a lower chamber enclosing a fluent mass of refractory heat trans-,

fer material and having a heat transfer material outlet at its lower end, said lower chamber having an inlet and outlet for afluid to be heated therein,

an unobstructed passage forming a throat of substantially reduced cross-section between said upper and lower chambers and enclosing a fluent enclosin a fluent mass .of refractory heat transfer material and having a heat transfer material inlet and a heatin gas outlet at its upper end, means for introducing heating gases directly into the lower part of said upper chamber in heat transfer relation with the mass of refractory material therein, a. lower chamber enclosing a fluent mass of "refractory heat transfer material and having a heat transfer material outlet at its lower end, said lower chamber having an inlet at its lower end for a gaseous fluid under pressure to-be heated therein and a gaseous fluid outlet at its upper end above the mass of heat transfer material therein, means forming a structurally unobstructed throat passage of substantially uniform reduced cross-section between and directly connecting said upper and lower chambers and enclosing a continuous fluent gaspervious column of refractory heat transfer material connecting said masses of refractory material in said upper and lower chambers, means receiving heat transfer material from said lower chamber material outlet and returning the material to said upper chamber material inlet, and means for controlling the relative pressures in said upper and lower chambers.

4. A fluid heater comprising an upper chamber enclosing a fluent mass of refractory heat transfer material and having a heat transfer material inlet and a heating gas outlet at its upper end, means for introducing high temperature heating gases into the lower part of said upper chamber in direct contact with the mass of heat transfer material therein, a lower chamber enclosing a fluent mass of refractory heat transfer material column of refractory heat transfer material connecting said masses of 'heat transfer material in i said upper and lower-chambers, and means for controlling the relative pressures in said upper andlower chambers in response to a variable condition in said throat. v I

6. A fluid heater comprising an upper chamber enclosing a fluent massof refractory pellets and having a pellet inlet and a heating gas outlet at its upper end, nieans for introducing heating gases into the lower part of said upper chamber in direct contact with the pellet mass therein, a lower chamber enclosing a, fluent mass of refractory pellets and having a pellet outlet at its lower end, said lower chamber having an inlet at its lower' end for a, fluid-to be heated therein under' pressure and a gaseous fluid outlet at its upper end, an unobstructed passage forming a. throat of, substantially reduced cross-section'between said-upper and lower chambers and enclosing a fluent mass of refractory pellets connecting said pellet masses in saidupper and lower chambers, means receiving pellets from said lower chamber pellet outlet'and returning'said pellets to said upper chamber pellet inlet, and means for conincluding a combustion chamber surrounding a said upper chamber and having a substantially annular inlet thereto. a lower chamber enclosing a fluent mass of refractory, pellets and having a pellet outlet at its lower end, said lower chamber having an inlet at its lower end for a gaseous fluid to be heated therein and a gaseous-fluid outlet at its upper and above the pellet mass therein,

means forming a structurally unobstructed throat passage of substantially reduced cross-section chamber and having a substantially annular heating gas inlet thereto, said upper chamber betweensaid upper and lower chambers and extending downwardly in said lower chamber to a level below said gaseous fluid outlet therefrom, said throat passage enclosing a fluent gas-pervious column of refractory pellets connecting said pellet masses in said upper and lower chambers, and

means receiving pellets from said lower chamber Y of circular cross-section enclosing a fluent mass of refractory heat transfer material and having a heat transfer material inlet and a heating gas outlet at its upper end, means for introducing v high temperature heating gases into the lower part of said upper chamber in direct contact with the mass of refractory material therein including a combustion chamber surrounding said upper chamber and having an annular bridge wall arranged to define a substantially annular heating gas inlet to said upper chamber, an annular baflle increasing incross-section above said annular inlet, refractory walls defining a vertically elonygated lower chamber of circular cross-section enclosing a fluent mass of refractory pellets and having a pellet outlet at its lower end, said lower chamber having an annular inlet chamber at its lower end for a gaseous fluid to be heated therein and a gaseous fluid outlet at its upper end above the pellet mass therein, a circular screen forming the inner side of said annular inlet chamber, and

a vertically elongated unobstructed passage forming a throat of substantially reduced cross-section between said upper and lower chambers and enclosing a fluent column of refractory pellets connecting said pellet masses in said upper and lower chambers.

' 11. A fluid heater comprising refractory walls defining a vertically elongated upper chamber of circular cross-section enclosing a fluent mass of refractory pellets and having a pellet inlet and upper end, and means forming an unobstructed throat passage of substantially reduced 'crosssection between said upper and lower chambers and enclosing a fluent column of refractory heat transfer material connecting said masses of refractory material in said upper and lower chambers.

9. A fluid heater comprising an upper chamber enclosing a fluent mass of refractory pellets and having a pellet inlet and a heating gas outlet at its upper end, means for introducing heating gases into thelower part of said upper chamber in direct contact with the pellet mass therein, a lower chamber enclosing a fluent mass of refractory pellets and having a pellet outlet at its lower end, said lower chamber having an annular inlet chamber at its lower end for a gaseous fluid to be heated therein and a gaseous fluid outlet at its upper end above the pellet mass therein, a

, screen forming'the inner side and terminating above the lower endtof said annular inlet chamber to form an outlet between said annular inlet chamber and said pellet outlet, and an unobstructed passage forminga throat of substantially reduced cross-section between said upper and lower chambers and enclosing a fluent mass of refractory pelletsconnecting said pellet masses in said upper and lower chambers.

10. A fluid heater comprising refractory walls defining a vertically elongated upper chamber of circular cross-section enclosing a fluid mass of refractory pellets and having a pellet inlet and a heating gas outlet at its upper end, means for introducing high temperature heating gases into the lower part of said upper chamber in direct contact with the pellet mass therein including a combustion chamber surrounding said upper a heating gas outlet at its upper end, means for introducing high temperature heating gases into the lower part of said upper chamber in direct contact with the pellet mass therein including a combustion chamber surrounding said upper chamber and having a substantially annular heating gas inlet thereto, said upper chamber increasing in cross-section above said annular inlet, refractory walls defining a vertically elongated lower chamber of circular cross-section enclosing a fluent mass of refractory pellets and having a pellet outlet at its lower end, said lower chamber having an annular inlet at its lower end for a gaseous fluid under pressure to be heated therein and a gaseous fluid outlet at its upper end above the pellet mass therein, a vertically elongated unobstructed passage forming a throat of substantially reduced cross-section between said upper and lower chambers and enclosing a fluent column of refractory pellets connecting said pellet masses in said upper and lower chambers, elevator 'means receiving pellets from said lower chamber pellet outlet and returning said pellet-s to said upper chamber pellet inlet including a rotary feeder constructed to form a gaseous fluid seal for said lower chamber material outlet, and means for controlling the relative pressures in said upper and lower chambers in response to variations in a condition indicative of gaseous fluid flow conditions in said throat.

12. A fluid heater comprising an upper chamber enclosing a fluent mass of refractory heat transfer material-and having a heat transfer material inlet and a heating gas outlet at its upper end, means for introducing heating gases under pressure at the lower end of said upper chamber, a lower chamber enclosing a fluent mass of refractory heat transfer material and having a heat transfer material outlet at its lower end, said lower chamber having an inlet at its lower end for a gaseous fluid under pres-sure to be heated therein and a gaseous fluid outlet at its upper end,

an unobstructed passage forming a throat of reduced cross-section between said upper and lower chambers and enclosing a fluent mass of refrac-' tory heat transfer material connecting said masses of refractory material in said upper and lower chambers, a control damper in one of said chamber gas outlets, and means responsive to variations in a pressure differential indicative of gaseous fluid flow conditions in said throat for actuating said damper to control the relative pressures in said upper and lower chambers.

13. A fluid heater comprising an upper chamber enclosing a fluent mass of refractory heat transfer material and having a heat transfer material inlet and a heating gas outlet at its upper end, means for introducing heating gases under 7 pressure at the lower end of said upper chamber,

a lower chamber enclosing a fluent mass of refractory heat transfer material and having a heat transfer material outlet at its lower end, said lower chamber having an inlet at its lower end for a gaseous fluid under pressure to be heated therein and a gaseous fluid outlet at its upper end, an unobstructed passage forming a throat of reduced cross-section between said upper and lower chambers and enclosing a fluent mass of refractory heat transfer material connectin said masses of refractory material in said upper and lower chambers, a control damper in said upper chamber heating gas outlet, and means responsive to the pressure diflerential across said throat for actuating said damper to control the relative pressures in said upper and lower chambers.

14. A fluid heater comprising walls defining an upper chamber enclosing a fluent mass of refractory pellets and having a heating gas outlet, means for introducing heating gases into said upper chamber in direct contact with the pellet mass therein, walls defining a lower chamber enclosing a fluent mass of refractory pellets and having a pellet outlet at its lower end, said lower chamber having an inlet and outlet for a fluid to be heated therein, a passage forming a throat of reduced cross-section between said upper and lower chambers and enclosing a fluent mass of refractory pellets connecting said pellet masses in said upper and lower chambers, transfer means arranged to receive pellets from said lower chamber and return said pellets to said upper chamber, and means for continuously controlling the supply of heating gases to said upper chamber in accordance with changes in a variable condition of the fluid leaving said lower chamber.

15. A fluid heater comprising walls defining an upper chamber enclosing a fluent mass of refractory pellets and having a heating gas outlet, means for introducing heating gases into said upper chamber in direct contact with the pellet mass therein, walls defining a lower chamber enclosing a fluent mass of refractory pellets and having a pellet outlet at its lower end, said lower chamber having an inlet and outlet for a gaseous fluid under pressure to be heated therein, an unobstructed passage forming a throat of reduced cross-section between said upper and lower chambers and enclosing a fluent mass of refractory pellets connecting said pellet masses in said upper and lower chambers, transfer means arranged to receive pellets from said lower chamber and return said pellets to said upper chamber, means for controlling the supply of gaseous fluid to said lower chamber in accordance with variations in the gaseous fluid outlet pressure from said lower chamber, and means for controlling the supply of heating gases to said upper chamber in accordance with variations in the temperature of the gaseous fluid leaving said lower chamber.

16; A fluid heater comprising walls defining an upper chamber enclosing a fluent mass of rciractory pellets and having a heating gas outlet, means for introducing heatin ases into said upper chamber in direct contact with the pellet mass therein, walls defining a lower chamber enclosing a fluent mass of refractory pellets and having a pellet outlet at its lower end, said lower chamber having an inlet at its lower end for a gaseous fluid under pressure to be heated therein and a gaseous fluid outlet at its upper end above the pellet mass therein, an unobstructed passage forming a throat of reduced cross-section between said upper and lower chambers and enclosing a fluent mass of refractory pellets connecting said pellet masses in said upper and lower chambers, transfer means arranged to receive pellets from said lower chamber and return said pellets to said upper chamber, means for controlling the relative pressures in said upper and lower chambers in accordance with variations in a condition indicative of gaseous fluid flow through said throat, means for controlling the supply of gaseous fluid to said lowerchamber in accordance with variations in the pressure of the fluid leaving said lower chamber, and means for controlling the supply of heating gases to said upper chamber in accordance with variationsin the temperature of the fluid leaving said lower chamber.

17. The method of controlling the flow of gaseous fluid under pressure between upper and lower chambers, each containing a gaseous fluid under pressure, having a structurally unobstructed connecting passage of reduced cross-section therebetween for the passage of a solid material which comprises maintaining a continuous gravity flow of a gas-pervious mass of solid material through said passage between said chambers, and controlling the relative gaseous fluid pressures in the chambers in accordance with changes in a variable operating condition in said passage from a predetermined value.

18. The method of operating apparatus having an upper chamber enclosing a fluent mass of solid material, a lower chamber enclosing a fluent mass of solid material, and an unobstructed throat of reduced cross-section connecting the upper and lower chambers and enclosing a fluent mass of solid material connecting the upper and.

lower chamber masses, which comprises maintaining a substantially continuous flow of solid material downwardly through the upper chamber, throat and lower chamber, continuously supplying a fluid under pressure to the upper chamber in direct contact with the solid material therein, continuously supplying a stream of fluid under pressure to the lower chamber in direct contact with the mass of solid material therein, separately withdrawing fluid from the upper and lower chambers, and controlling the relative pressures in the upper and lower chambers in accordance with variations in a condition responsive to fluid flow through the throat.

19. The method of operating apparatus having an upper chamber enclosing a fluent mass of solid material, a lower chamber enclosing a fluent mass of solid material, and an unobstructed throat of reduced cross-section connecting the upper and lower chambers and enclosing a fluent column of solid material connecting the upper and lower chamber masses, which comprises maintaining a substantially continuous flow of solid material downwardly through the upper chamber, throat, and lower chamber, continuously supplying a gaseous fluid under pressure to the upper chamber in direct contact with the solid material therein, continuously supplying a stream of gaseous fluid under pressure to the lower chamber in direct contact with the solid fluid from the upper and lower chambers, co

trolling the relative pressures in the upper and refractory heat transfer material, an unobstructed throat of reduced cross-section connecting the upper and lower chambers and enclosing a fluent mass of the refractory heat transfer material connecting the upper and lower chamber masses, and transfer means arranged to receive heat transfer material from the lower chamber and return said material to the upper chamber, which comprises maintaining a substantially continuous circulation of said heat transfer material downwardly through the upper chamber, throat, and lower chamber, continuously heating the heat transfer material while in the upper chamber to a high temperature by direct contact with an ascending stream of heating gases, continuously passing a stream of gaseous fluid under pressure upwardly through the lower chamber in direct contact with the heat transfer material therein, withdrawing the chamber and return said material to the upper chamber, which comprises maintaining a substantially continuous circulation of said heat heated gaseous fluid at the upper end of the lower chamber, and controlling the relative pressures in the upper and lower chambers to maintain the gaseous fluid flow through the throat at a pre determined value.

21. The method of operating a fluid heater having an upper chamber enclosing a fluent mass of refractory heat transfer material, a lower chamber enclosing a fluent mass of the refractory heat transfer material, an unobstructed throat of reduced cross-section connecting the upper,

and lower chambers and enclosing a fluent mass of the refractory heat transfer material connecting the upper and lower chamber masses, and transfer means arranged to receive heat transfer material from the lower chamber and return said material to the upper chamber, which comprises maintaining a substantially continuous circulation of said heat transfer material downwardly through the upper chamber, throat, and lower chamber, continuously heating the heat transfermaterial while in the upper chamber by direct contact with a heating fluid therein, continuously supplying a stream of fluid to be heated to the lower chamber in direct contact with the mass of heat transfer material therein, separately withdrawing fluids from the upper and lower chambers, and controlling the rate of supply of heating fluid to the upper chamber in accordance with variations in the temperature of the fluid leaving the lower chamber from a predetermined value.

22. The method of continuously heating a gaseous fluid to a high temperature in a fluid heater having an upper chamber enclosing a fluent mass of refractory heat transfer material, a lower chamber enclosing a fluent mass of the refractory 'heat transfer material, an unobstructed throat of reduced cross-section connecting the upper and lower chambers'and enclosing a fluent mass of the refractory heat transfer material connecting the upper and lower chamber masses, and transfer means arranged to receive heat transfer material from the lower transfer material downwardly through the upper chamber, throat, and lower chamber, continuously heating the heat transfer material while in the upper chamber to a high temperature by direct contact with an ascending stream of heating gases, continuously passing a stream of gaseous fluid to be heated upwardly through the lower chamber in direct contact with the mass of heat transfer material therein, withdrawing the heated gaseous fluid at the upper end of the lower chamber, controlling the relative pressures in the upper and lower chambers in accordance with variations in the pressure differential across the throat from a predetermined value, and controlling the supply of gaseous fluid to the lower chamberin accordance with variations in the outlet pressure of the gaseous fluid in the lower chamber from a predetermined value.

23. A fluid heater comprising an upper chamber confining a fluent gas-pervious mass of refractorypellets and having a pellet inlet and a heating gas outlet at its upper end, means for introducing heating gases directly into the lower :part of said upper chamber in direct contact with the pellet mass therein, a lower chamber confining a fluent gas-pervious mass of refractory pellets and having a pellet outlet at its lower end, said lower chamber having an inlet and outlet for a gaseous fluidto be heated therein, means forming a vertically elongated structurally unobstructed passage defining a throat of substantially uniform reduced cross-section between and directly connecting said upper and lower chambers and conflning a fluent gas-pervious column of refractory pellets connecting said pellet masses in\said upper and lower chambers, and means receiving pellets from said lower chamber pellet outlet and returning said pellets to said upper chamber pellet inlet, a control damper arranged to control the gas flow through one of said chambers, damper actuating means connected to said damper, and means automatically responsive to variations in-the pressure differential across said throat from a predetermined value for operating said damper actuating means.

let for a fluid to be heated therein, means forming a vertically elongated structurally unobstructed passage defining a throat of substantially uniform reduced cross-section between and directly connecting said upper and lower chambers and confining a fluent gas-pervious column of refractory heat transfer material connecting said masses of heat transfer material in said upper and lower chambers, means receiving said heat transfer material from said lower chamber material outlet and returning said heat transfer material to said upper chamber material inlet, and means forautomatically controlling the relative pressures in said upper and lower chambers in 21 response to variations in a variable condition in Number said throat. 1,803,081 ERVIN G. BAILEY. 1,843,566 RALPH M. HARDGROVE. 1,871,166 5 2,252,368 REFERENCES CITED 2 254 4 1 The following references are of record in the 2,304,397 file of this patent: 2 3

UNITED STATES PATENTS 10 Number Name Date 220,191 Tatham Sept. 30, 1879 Number 1,148,331 Olsson July 27, 1915 212,671 1,178,667 Nlewerth Apr. 11, 1916 1,203,944 Weber Nov, 7, 1916 15 636,892 1,614,387 Pereda Jan. 11, I927 22 Name Date Uhle et a1. Apr. 28, 1931 Lake Feb. 2, 1932 Fahnbach Aug. 9, 1932 Germer Aug. 12, 1941 Harris Sept. 2, 1941 Campbell Dec. 8, 1942 Conn Aug. 17, 1943 Saathofi' Aug. 31, 1943 FOREIGN PATENTS Country Date England Mar. 20,1924 England Aug. 23, 1940 Germany Apr. 28, 1937 Certificate of Correction Patent No. 2,447,306 August 17, 1948 ERVIN G. BAILEY ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 5, line 1, after the word spilling insert over; line 52, for lestic reed plastic; column 20, line 40, before means strike out and;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice. Signed and sealed this 20th day of December, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

